The development of high-brightness solid state light sources, such as but not limited to light emitting diodes (LEDs), has led to use of such devices in various lighting fixtures. In general, an LED is a current driven device, i.e. the brightness of the light output of an LED may be directly related to the current supplied to the LED. However, the current through an LED should be limited to a design maximum to avoid over-current damage or failure of the LED.
To achieve controlled luminance and to prevent over-current failure of an LED or string of series-connected LEDs, it is known to drive the LED(s) through a linear current regulator using a constant voltage source. The constant voltage source may provide a constant output voltage at an input to the linear current regulator. In response to the output of the constant voltage source, the linear current regulator may provide a constant output current to the LED(s). The LED(s) may thus be driven at a constant current, even with changes in the forward voltage drop across the LED(s), e.g. due to environmental conditions, aging, or other variances from a nominal voltage drop.